Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  mm/shrinker: fix bogus set_shrinker_bit() with cgroup.memory=nokmem  With cgroup.memory=nokmem, shrinker_memcg_alloc() bails out early and never allocates an id, so shrinker->id keeps the 0 it got from the kzalloc() in shrinker_alloc().  __list_lru_init() then copies that 0 into lru->shrinker_id, where it looks like a valid bit index.  Nothing calls expand_shrinker_info() on nokmem either, so shrinker_nr_max stays 0 and every memcg ends up with an empty map (map_nr_max == 0).  deferred_split_folio() hands a real memcg to __list_lru_add() regardless of whether the lru is memcg aware, so the first THP queued in a cgroup does set_shrinker_bit(memcg, nid, 0) and trips the bounds check:  WARNING: mm/shrinker.c:212 at set_shrinker_bit+0x7d/0x90, CPU#126 Call Trace:  <TASK>  deferred_split_folio+0x18c/0x220  map_anon_folio_pmd_nopf+0xdd/0x130  map_anon_folio_pmd_pf+0x14/0xb0  do_huge_pmd_anonymous_page+0x1a1/0x620  __handle_mm_fault+0xea9/0x10d0  handle_mm_fault+0xe5/0x320  do_user_addr_fault+0x1cc/0x870  exc_page_fault+0x81/0x1b0  asm_exc_page_fault+0x27/0x30  </TASK>  Harmless, the WARN_ON_ONCE() is what keeps the out of bounds unit[] read from happening, but the id should not look valid in the first place.  Clear it before returning.  Two other spots could paper over this: drop the id in __list_lru_init() when nokmem turns memcg_aware off, or make deferred_split_folio() pass NULL like list_lru_add_obj() does.  Both leave shrinker->id lying around for the next caller, so fix it where the id is handed out.
Data source: kernel.org (416baaa9-dc9f-4396-8d5f-8c081fb06d67)